The invention is in the field of liquid crystal display (LCD) devices such as active matrix LCDS (AMLCDs), and relates more particularly to light shielding in such devices.
Reflective LCD devices per se are known to those of ordinary skill in this art. Such devices generally include an array of reflective pixels over a silicon substrate, with various wiring or metal layers and other elements located between the reflective pixels and a surface of the silicon substrate, and typically within an insulating layer of oxide.
A cross-section of a typical reflective LCD device is shown and described in a paper entitled "High Resolution and Brightness LCD Projector With Reflective LCD Panels" by Sato, Yagi and Hanihara of the Pioneer Corporation, Japan. A cross-section of a portion of a typical prior-art reflective LCD is shown in FIG. 3 of that paper, and a representation of that figure is shown in prior-art FIG. 1 of the instant application for convenience. With reference to the following description, familiarity with conventional features of such devices will be assumed, so that only features bearing on the present invention will be described.
Typical prior-art reflective LCD devices, such as the representative device 8 shown in FIG. 1, are typically composed, in relevant part, of a silicon substrate 10, on which are successively provided an oxide layer 12, a liquid crystal layer 14, an ITO electrode 16 and a glass layer 18. An array of pixel electrodes 20 is provided beneath the liquid crystal layer 14 in the oxide layer 12, with light transmissive regions 22 being located between the reflective pixel electrodes 20. Also provided in the oxide layer 12 and between the pixels 20 and the substrate 10 are three metal layers 24, 26 and 28. The metal layers 26 and 28 form mutually-orthogonal row and column lines, which may be connected to gate and source electrodes of MOS transistors (not shown in FIG. 1) fabricated in the underlying silicon substrate 10. In addition to these two metal layers, the third metal layer 24 is provided beneath the light transmissive regions 22 between the reflective pixels 20 to prevent light entering the device through such transmissive regions between the reflective pixels from reaching the substrate, where it might induce leakage currents on otherwise interfere with proper device operation. Note that while portions of layers 26 or 28 may incidentally block a small portion of light entering the device, the structure of FIG. 1 requires a separate metal layer to provide the required degree of light blocking. While this prior-art solution is satisfactory from a functional viewpoint, it requires an additional dedicated metal layer in the device structure, thus increasing complexity, fabrication time and cost, while decreasing reliability due to the increased complexity and greater likelihood of a short circuit.
Accordingly, it would be desirable to accomplish the light-blocking function of the dedicated metal layer in the prior art devices without the necessity for a separate metal layer provided solely for this purpose.